Multifunctional Lubricant Additive Package for a Rough Mechanical Component Surface

ABSTRACT

The present invention provides a multifunctional lubricant additive or composition for improving load-carrying capacity, scuffing (scoring) resistance, and other performance characteristics of a lubricant. The composition includes a friction modifier, an antiwear additive, an extreme pressure additive, and a surface fatigue life modifier. The present invention further provides a method for improving the performance characteristics of a lubricant, which includes a step of mixing a lubricant base oil or fully formulated lubricant with the above-described multifunctional lubricant additive composition.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional Application No. 60/625,416 filed Nov. 4, 2004, and is related to the following co-pending and commonly-owned applications which were filed herewith and are hereby incorporated by reference in full: “Lubricant Additive Packages for Improving Load-Carrying Capacity and Surface Fatigue Life” (Attorney Docket No. 0002290WOU, EH-11605), U.S. Ser. No. ______; “Multifunctional Lubricant Additive Package” (Attorney Docket No. 0002291WOU, EH-11679), U.S. Ser. No. ______; “Lubricants Containing Multifunctional Additive Packages Therein for Improving Load-Carrying Capacity, Increasing Surface Fatigue Life and Reducing Friction” (Attorney Docket No. 0002294WOU, EH-11697), U.S. Ser. No. ______.

GOVERNMENT RIGHTS IN THE INVENTION

The invention was made by, or under contract with the National Institute of Standards and Technology of the United States Government under contract number: 70NANB0H3048.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multifunctional lubricant additive composition or package for improving the performance characteristics of a lubricant. More particularly, the present invention relates to a multifunctional lubricant additive composition or package for providing a lubricant with superior performance characteristics such as improved load-carrying ability, anti-scuffing (anti-scoring) capacity, friction reduction, and improved surface-fatigue life.

2. Description of Related Art

Mechanical systems such as manual or automatic transmissions; single and multi-speed aviation transmissions, including but not limited to those used to propel rotorcraft and those used to alter the rotational speed of the sections within gas turbine engines; push-belt type continuous variable transmissions; and traction drive continuous variable transmissions, have large surface areas of contact portions or zones. These contact portions or zones, such as drive rolling surfaces, and gear and ball- and roller bearings, are known to be susceptible to high surface pressures. In addition, internal combustion engines and other propulsion devices, especially those that are common for high-performance and racing applications, are subject to taxing demands in the form of inertial loading, high sliding and/or rolling speeds, and marginal lubrication. Moreover, the need for reducing friction, resistance, and fatigue within larger contact zones of mechanical systems is increased by many recently developed transmission systems that are designed to be miniaturized or weight-reduced to maximize transmission throughput capacity.

To address these severe application demands, lubricants, especially those containing specific additives, play a critical role in protecting and minimizing the wear and scuffing (scoring) of surfaces. The lubricants generally reduce principal damage accumulation mechanisms of lubricated components caused by surface fatigue and overloading.

Examples of known lubricants are discussed in the following publications, which are hereby incorporated in full by reference: Phillips, W. D., Ashless phosphorus-containing lubricating oil additives; Lubricant Additives Chemistry and Application 45-111 (L. R. Rudick, Marcel Dekker, Inc. 2003); and Kenbeck, D. and T. F. Buenemann, Organic Modifiers; Lubricant Additives Chemistry and Application 203-222 (L. R. Rudick, Marcel Dekker, Inc. 2003).

Recently developed system-optimization approaches for increasing overall power throughput of mechanical systems, underscore the need for new and better performing lubricant additives. By reducing friction, wear, pressure, and improving scoring (scuffing) resistance, these additives prolong surface fatigue life for lubricated contacts within transmission systems and propulsive devices.

The present invention provides lubricant additives for improving the performance characteristics (i.e., load capacity and/or surface fatigue life, etc.) of mechanical systems. Combining the additive composition provided by this invention with lubricant stocks, and optionally other additives, results in a fully formulated lubricant with many performance advantages such as reduction in friction and wear and increasing the surface fatigue life.

SUMMARY OF THE INVENTION

The present invention provides a lubricant additive comprising elements or components that are intended to enhance the performance characteristics of a lubricant base stock or fully formulated lubricant including anti-wear (AW), extreme pressure (EP), friction modifying (FM), and surface fatigue life (SFL) modifying compositions.

In a preferred embodiment, this invention provides a multifunctional lubricant additive composition for improving the performance characteristics of a natural or synthetic lubricant for use in transmission fluid products that meet both civil and military specifications.

In another embodiment, the present invention provides a multifunctional composition for use in improving performance of metals and alloys of power transmission components, including gears, bearings, splines, shafts and springs.

In another embodiment, this invention provides a multifunctional lubricant additive composition for improving the performance characteristics of engines and related propulsive devices used to power automobiles, both stock (production) and specialty (e.g. racing and other high performance) varieties, and heavy on- and off-road equipment, such as farm implements and construction equipment.

In another embodiment, the present invention provides a multifunctional lubricant additive composition capable of being combined with lubricant stocks and other additives to produce a fully formulated lubricant that beneficially reduces friction and scuffing (scoring), and increases resistance to surface degradation, including but not limited to, fatigue including micro and macro pitting, and wear.

In yet another embodiment, the present invention provides a multifunctional lubricant additive composition for improving the performance characteristics of a lubricant, which includes one or more of the following components:

(a) a friction modifier of a long-chain partial ester having the general formula:

wherein R¹ and R² are each a C_(i)H_(2i+1) alkyl group and where i is an integer of about 7≦i≦15;

(b) an antiwear additive consisting of an alkyl neutral phosphate or an aryl neutral phosphate of the general formula:

wherein R³, R⁴, and R⁵ are each independently a C_(n)H_(2n+1) alkyl group or C₆H₅C_(m)H_(2m+1) aryl group, n is an integer of about 2≦n≦10, and m is an integer of about 0≦m≦8; and

(c) an extreme pressure additive consisting of an alkyl phosphite, an aryl phosphite, or a mixture of an alkyl phosphite and an aryl phosphite having the general formula:

wherein R⁶, R⁷, R⁸, R⁹, R¹⁰, and R¹¹ are each C_(j)H_(2j+1) alkyl groups having tertiary structures, where j is an integer of about 1≦j≦about 20; and a phenol compound having the general formula:

wherein R¹², R^(12′), R^(12″), and R^(12′″) are each independently a normal C_(p)H_(2p+1) alkyl group, and p is an integer of about 1≦p≦12, where R¹³, R^(13′), R^(13″), and R^(13′″) are each independently a phenol group having the formula:

wherein R¹⁴, R¹⁵, and R¹⁶ are each independently a C_(o)H_(2o+1) alkyl group and o is an integer of about 1≦o≦20, and where R¹⁵ and R¹⁶ are tertiary structures; and

(d) a surface fatigue life modifier comprising alkylthiocarbamoyl groups having the general formula:

wherein R¹⁷, R¹⁸, R¹⁹, and R²⁰ are each independently C_(k)H_(2k+1) alkyl groups and k is an integer of about 1≦k≦30, and wherein R¹⁷, R¹⁸, R¹⁹, and R²⁰ optionally form a ring structure as combined together with the nitrogen atom to which they are bonded, where (A) is a chain of sulfur atoms, S_(n), or generally represented by the formula:

S—(CH₂)_(m)—S

and n and m are integers of about 1≦n≦10, and about 1≦m≦6.

The present invention also provides a method for improving the performance characteristics of a lubricant. The method includes mixing a lubricant with the above-described multifunctional lubricant additive composition.

The present invention also shows that the above-described multifunctional lubricant additive composition can improve the performance characteristics of a lubricant, especially the scuffing (scoring) resistance thereof.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE shows the relationship between the average traction (friction) coefficient and average load stage for various lubricants. The vertical arrows indicate the average scuffing (scoring) failure load stage (load-carrying capacity) of the formulated lubricants. A higher scuffing (scoring) failure load stage indicates a greater load-carrying capacity of the lubricant.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a multifunctional lubricant composition for improving the performance characteristics of a lubricant, especially its ability to enhance scuffing (scoring) resistance of mechanical component surfaces. The composition includes one or more, and preferably all of the following component surfaces: (a) a friction modifier (FM); (b) an antiwear (AW) additive; (c) an extreme pressure (EP) additive; and (d) a surface fatigue life (SFL) modifier. The total amount of additives (a)-(d) is preferably about 10% by mole or less based on the total amount of lubricant.

The above components of the lubricant composition are further described below. In a preferred embodiment, the composition includes the following:

(a) a friction modifier of a long-chain ester having the general formula:

wherein R¹ and R² are each a C_(i)H_(2i+1) alkyl group and where i is an integer of about 7≦i≦15, preferably about 8≦i≦10;

(b) an antiwear additive consisting of an alkyl neutral phosphate or an aryl neutral phosphate of the general formula:

wherein R³, R⁴, and R⁵ are each independently a C_(n)H_(2n+1) alkyl group or a C₆H₅C_(m)H_(2m+1) aryl group, n is an integer of about 2≦n≦10, and m is an integer of about 0≦m≦8; preferably about 4≦n≦6 and 1≦m≦5, and

(c) an extreme pressure additive consisting of an alkyl phosphite, an aryl phosphite, or a mixture of an alkyl phosphite and an aryl phosphite having the general formula:

wherein R⁶, R⁷, R⁸, R⁹, R¹⁰, and R¹¹ are each C_(j)H_(2j+1) alkyl groups having tertiary structures, where j is an integer of about 1≦j≦about 20, preferably about 4≦j≦about 8; and a phenol compound having the general formula:

wherein R¹², R^(12′), R^(12″), and R^(12′″) are each independently a normal C_(p)H_(2p+1) alkyl group, and p is an integer of about 1≦p≦12, preferably about 1≦p≦5, where R¹³, R^(13′), R^(13″), and R^(13′″) are each independently a phenol group having the formula:

wherein R¹⁴, R¹⁵, and R¹⁶ are each independently a C_(o)H_(2o+1) alkyl group and o is an integer of about 1≦o≦20, preferably about 2≦o≦10, and where R¹⁵ and R¹⁶ are tertiary structures; and

(d) a surface fatigue life modifier comprising alkylthiocarbamoyl groups having the general formula:

wherein R¹⁷, R¹⁸, R¹⁹, and R²⁰ are each independently a C_(k)H_(2k+1) alkyl group and k is an integer of about 1≦k≦30, preferably about 4≦k≦8, and wherein R¹⁷, R¹⁸, R¹⁹, and R²⁰ optionally form a ring structure as combined together with the nitrogen atom to which they are bonded, where (A) is chain of sulfur atoms, S_(n), or generally represented by the formula:

S—(CH₂)_(m)—S

and n and m are integers of about 1≦n≦10 and about 1≦m≦6; preferably about 1≦n≦6 and about 1≦m≦3.

In a preferred embodiment, component (a), the friction modifier of the composition, is present in a concentration from about 0.2% to 6% by mole, and preferably from about 0.6% to 2% by mole, based on the total amount of lubricant. An example of a friction modifier is glycerol monooleate.

Component (b), the antiwear additive of the composition, is present in a concentration from about 0.1% to 5% by mole, preferably from about 0.2% to 2% by mole, based on the total amount of lubricant. An example of an antiwear additive is tricresyl phosphate.

Component (c), the extreme pressure additive of the composition, includes compound (III), an aryl or alkyl phosphite in an amount from about 0.05% to 4.5% by mole, preferably from about 0.18% to 1.8% by mole, based on the total amount of lubricant. An example of the extreme pressure additive compound (III) which can be used in the composition is tris-(2,4-di-tertiary-butyl-phenyl)phosphite. In this embodiment, component (c) further includes compound (IV), a phenol compound, which is present in an amount from about 0.005% to 1% by mole, preferably from about 0.02% to 0.3% by mole, based on the total amount of the lubricant. An example of the extreme pressure additive compound (IV) is tetrakis-(methylene-3,5-di-tert-butyl-4-hydroxy hydrocinnamate) methane.

Component (d), the surface fatigue life modifier of the composition, is present in a concentration from about 0.1% to 6% by mole, preferably from about 0.1% to 3% by mole, based on the total amount of lubricant. Moreover, the total concentration of all four additives (a)-(d) is preferably about 10% or less by mole based on the total amount of lubricant.

In a preferred embodiment, the ratio of the amount of all four additives: the friction modifier, the antiwear additive, the extreme pressure additive, and the surface fatigue life modifier is about 2:1:1:0.5.

An optimal embodiment of the resulting lubricant containing the above additives would provide a mechanical component with a surface roughness of about 3 to 10 microinches.

Lubricants that the present invention can improve include but are not limited to gear oil, bearing oil, sliding surface lubrication oil, chain lubricating oil, and engine oil. In a preferred embodiment, various types of lubricants, greases, especially synthetic polyol ester (POE) based lubricants, can be used as the lubricating materials. Moreover, a skilled artisan would recognize that the embodiments of this invention are not limited to the above oils of the polyol ester type, but also apply to other compositions and oils including but not limited to mineral oil based lubricants (hydrocarbon-based), polyalkylene glycol (PAG), aromatic napthalene (AN), alkyl benzenes (AB), and polyalphaolefin (PAO) types.

The present invention is useful as an additive composition for natural and synthetic aviation (aerospace) and automotive lubricants. A combination of the multifunctional additive composition with the above-described lubricants improves transmission power throughput and system power density.

Specific uses also include turbine engine and transmission oils designed to meet government civil (FAA) and military (DoD) specification and requirements. Additional uses of the multifunctional additive composition include the demonstrated ability to improve scuffing (scoring) performance of metals and alloys that are commonly used for power transmission components, including but not limited to gears, bearing, splines shafts, and springs. As such, these improvements decrease the incidence of component and system failure and rejection during customer acceptance test protocols (ATP). The additive composition also improves pitting (surface) fatigue life and reduces the rate of component and system degradation due to wear and other phenomena, and may improve the surface fatigue life of mechanical components.

In another embodiment, the present invention provides a method of improving the performance characteristics of a lubricant, especially the scuffing (scoring) performance of mechanical components protected thereby. The method comprises the step of:

mixing a lubricant, or lubricant base stock, with a multifunctional lubricant additive composition that includes at least one of compounds (a)-(d) of the above-described lubricant additive composition thereby producing a fully formulated lubricant. For this embodiment, the molar concentration of compounds (a)-(d) may be varied to achieve a desired effect, provided however, that the total amount of the four additives, is about 10% by mole or less based on the total amount of lubricant.

The following are examples and tables that include experimental results intended to illustrate preferred embodiments of the multifunctional additive composition.

Formulation #5

This example used Exxon-Mobil Jet Oil II, a standard (STD) version of MIL-PRF-23699 5 cSt gas turbine oil, which typically has excellent lubricant performance compared to other brands and versions of MIL-PRF-23699 oil. By adding the lubricant additive of the present invention to the Exxon-Mobil Jet Oil II, the resulting load carrying capacity increased about 1.29 times, as shown in the FIGURE and Table 2. Also, the traction (friction) coefficient of Formulation #5 was lower than that of Exxon-Mobil Jet Oil II. The addition of the lubricant additive resulted in a slight increase of the polishing wear, thereby reducing roughness, which is beneficial to the surface initiated fatigue or micropitting resistance.

Experimental Results

These Experimental Results were obtained using a generally accepted modified variation of the Wedeven Associates, Inc. WAM Load Capacity Test Method (“WAM Test”). The WAM Test is designed to evaluate the loading capacity of lubricants and load bearing surfaces evaluating the wear, tear and scuffing (scoring) thereof over a large temperature range. For a detailed description of the WAM Test, see WAM Load Capacity Test Method, SAE Aerospace AIR4978, Revision B, 2002, and U.S. Pat. No. 5,679,883 to Wedeven, L D, incorporated herein by reference.

High load-carrying oils frequently result in test suspension at load stage 30 without a scuffing (scoring) event. To differentiate candidate formulations that reach test suspension, tests can be run with a modified test protocol. The modified protocol operates at a lower entraining velocity than the standard test protocol. The lower entraining velocity, which reduces the EHD film thickness, increases the test severity by causing greater asperity interaction. The test essentially operates at a reduced film thickness to surface roughness (h/σ) ratio.

The modified test protocol was developed for high load-carrying oils used for aviation gearboxes. These oils include the DOD-PRF-85734 oils for the U.S. Navy and the Def Stan 91-100 oils for the U.K. Ministry of Defense. With the modified test protocol, the highest load-carrying oils currently used in military aircraft experience scuffing (scoring) failures at load stages that range from approximately 19 to approximately 28.

Table 1 below shows a summary of WAM Test conditions that were utilized to test various lubricants of this invention.

TABLE 1 Ball: AISI 9310; Ra: 10-12 μin Rolling Velocity: 158 in/sec Disc: AISI 9310; Ra: 6 μin Sliding Velocity: 345 in/sec Ball Velocity: 234 in/sec Entraining Velocity: 158 in/sec Disc Velocity: 234 in/sec Velocity Vector Angle (Z): 95° Disc Hardness: 62.5-63.5 HRC Temperature: Ambient (~22° C.) Ball Hardness: 62.5-63.5 HRC

The reference lubricant for this study, Exxon-Mobil Jet Oil II, contains tricresyl phosphate, which is one example of an anti-wear (AW) additive. As such, only the friction modifier, extreme pressure additive, and surface fatigue life modifier were mixed with the Exxon-Mobil Jet Oil II to form Formulation #5. The scuffing (scoring) performance results are shown in Table 2.2. The average scuffing (scoring) failure stage of Formulation #5 was 24.75, which is about 1.29 greater than that of the Exxon-Mobil Jet Oil II, which had an average scuffing (scoring) failure stage of 19.2.

Table 2.1 below shows additives used in Formulation #5.

TABLE 2.1 Additive mole % Supplier Friction Glycerol Monooleate 1.0 Crompton Modifier Extreme Tris-(2,4-di-tertiary- 0.45 Strem Pressure butyl-phenyl) Phosphite Chemicals Additive Pentaerythritol Tetrakis- 0.05 Sigma- (methylene-3,5-di-tert- Aldrich butyl-4-hydroxyhydrocinnamate) Surface Fatigue Tetra-n-butylthiuram 0.35 R T Life Modifier Vanderbilt

Table 2.2 below is a comparison of the experimental results for the commercial lubricant Exxon-Mobil Jet Oil II and Formulation #5. The ball and disc were composed of AISI 9310 and had a surface hardness of R_(C) 63 (63 HRC).

TABLE 2.2 Average Increased Macro- Scuffing Load- scuff (Scoring) Carrying Micro-scuff (score) Failure Capacity Lubricant Ball Disc/t.d. (score) Stage Stage Stage Factor Exxon-Mobil Jet Oil II SBAD12-9a 9-10a/3.7 25 Exxon-Mobil Jet Oil II SBAD12-9b 9-10a/3.6 15 Exxon-Mobil Jet Oil II UTLCC3-9a 9-10a/3.5 24 Exxon-Mobil Jet Oil II UTLCC3-9b 9-10a/3.4 25 Exxon-Mobil Jet Oil II UTLCC5-9a 9-10a/3.3 7 15 19.2 1 Formulation #5 UTLCC19-9a 9-26a/3.5 23 Formulation #5 UTLCC19-9b 9-26a/3.4 27 Formulation #5 UTLCC21-9a 9-26a/3.3 24 Formulation #5 UTLCC21-9b 9-26a/3.2 25 24.75 1.29

While the embodiments described above are directed to lubricants of the polyol ester (POE) type, a skilled artisan would recognize that the compositions apply equally to other lubricant stock compositions including, but not limited to, lubricants comprising grease, mineral (hydrocarbon-based), polyalkylene glycol (PAG), aromatic naphthalene (AN), alkyl benzenes (AB) and polyalphaolefin (PAO) types.

It should therefore be understood that the foregoing description is only illustrative of the present invention. A skilled artisan, without departing from the present invention, can devise various alternatives and modifications. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variations that fall within the scope of the appended claims. 

1. A multifunctional lubricant additive package for improving the performance characteristics of a lubricant, said composition comprising: a friction modifier comprising a long-chain ester represented by the formula:

wherein R¹ and R² are each independently a normal C_(i)H_(2i+1) alkyl group, and wherein i is an integer of about 7≦i≦15.
 2. A composition according to claim 1, wherein i is about 8≦i≦10.
 3. A composition according to claim 1, further comprising an antiwear additive comprising an alkyl neutral phosphate or an aryl neutral phosphate represented by the formula:

wherein R³, R⁴, and R⁵ are each independently a C_(n)H_(2n+1) alkyl group of an alkyl neutral phosphate or a C₆H₅C_(m)H_(2m+1) aryl group of an aryl neutral phosphate, wherein n is an integer of about 2≦n≦10 and wherein m is an integer of about 0≦m≦8.
 4. A composition according to claim 3, wherein n is about 4≦n≦6.
 5. A composition according to claim 3, wherein m is about 1≦m≦5.
 6. A composition according to claim 3, further comprising an extreme pressure additive consisting of a combination of (a) at least one of an alkyl phosphite and an aryl phosphite, and (b) a phenol compound, wherein the alkyl or aryl phosphite is represented by the formula:

wherein R⁶, R⁷, R⁸, R⁹, R¹⁰, and R¹¹ are each independently C_(j)H_(2j+1) alkyl groups exhibiting tertiary structures, where j is an integer of about 1≦j≦20, wherein the phenol compound is represented by the formula:

wherein R¹², R^(12′), R^(12″), and R^(12′″) are each independently C_(p)H_(2p+1) alkyl groups and p is an integer of about 1≦p≦12; wherein R¹³, R^(13′), R^(13″), and R^(13′″) are each independently a phenol group represented by the formula:

wherein R¹⁴, R¹⁵, and R¹⁶ are each independently a C_(o)H_(2o+1) alkyl group and o is an integer of about 1≦o≦20, wherein R¹⁵ and R¹⁶ are tertiary structures.
 7. A composition according to claim 6, wherein j is about 4≦j≦8.
 8. A composition according to claim 6, further comprising a surface fatigue life modifier comprising an alkylthiocarbamoyl group represented by the formula:

wherein R¹⁷, R¹⁸, R¹⁹, and R²⁰ are each independently a C_(k)H_(2k+1) alkyl group and k is an integer of about 1≦k≦30, wherein R¹⁷, R¹⁸, R¹⁹, and R²⁰ optionally form a ring structure as combined together with the nitrogen atom to which they are bonded, where (A) is a chain of sulfur atoms, S_(n), or represented by the formula: S—(CH₂)_(m)—S and wherein n and m are integers of about 1≦n≦10 and about 1≦m≦6.
 9. The composition according to claim 3, wherein n of the antiwear additive is an integer of about 4≦n≦6 and m is an integer of about 1≦m≦5.
 10. The composition according to claim 6, wherein j of the extreme pressure additive is an integer of about 4≦j≦8, p is an integer of about 1≦p≦5, and o is an integer of about 2≦o≦10.
 11. The composition according to claim 1, wherein the friction modifier is glycerol monooleate.
 12. The composition according to claim 1, wherein the friction modifier is present in an amount from about 0.2% to 6% by mole based on the total amount of lubricant.
 13. The composition according to claim 1, wherein the friction modifier is present in an amount from about 0.6% to 2% by mole based on the total amount of lubricant.
 14. The composition according to claim 3, wherein the antiwear additive is tricresyl phosphate.
 15. The composition according to claim 3, wherein the antiwear additive is present in an amount from about 0.1% to 5% by mole based on the total amount of lubricant.
 16. The composition according to claim 3, wherein the antiwear additive is present in an amount from about 0.2% to 2% by mole based on the total amount of lubricant.
 17. The composition according to claim 6, wherein the extreme pressure additive compound (III) is tris-(2,4-di-tertiary-butyl-phenyl) phosphite.
 18. The composition according to claim 6, wherein the extreme pressure additive compound (III) is present in an amount from about 0.05% to 4.5% by mole based on the total about of lubricant.
 19. The composition according to claim 6, wherein the extreme pressure additive compound (III) is present in an amount from about 0.18% to 1.8% by mole based on the total about of lubricant.
 20. The composition according to claim 6, wherein the extreme pressure additive compound (IV) is present in an amount from about 0.005% to 1% by mole based on the total about of lubricant.
 21. The composition according to claim 6, wherein the extreme pressure additive compound (IV) is present in an amount from about 0.02% to 0.3% by mole based on the total about of lubricant.
 22. The composition according to claim 6, wherein the extreme pressure additive compound (IV) is tetrakis-(methylene-3,5-ditert-butyl-4-hydroxy hydrocinnamate) methane.
 23. The composition according to claim 8, wherein the surface fatigue life modifier is present in an amount from about 0.1% to 6% by mole based on the total amount of lubricant.
 24. The composition according to claim 8, wherein the surface fatigue life modifier is present in an amount from about 0.1% to 3% by mole based on the total amount of lubricant.
 25. A multifunctional lubricant composition for improving the performance characteristics of a lubricant, said composition comprising: a base stock; a friction modifier comprising a long-chain ester represented by the formula:

 wherein R¹ and R² are each independently a normal C_(i)H_(2i+1) alkyl group, and wherein i is an integer of about 7≦i≦15; an antiwear additive comprising an alkyl neutral phosphate or an aryl neutral phosphate represented by the formula:

wherein R³, R⁴, and R⁵ are each independently a C_(n)H_(2n+1) alkyl group of an alkyl neutral phosphate or a C₆H₅C_(m)H_(2m+1) aryl group of an aryl neutral phosphate, wherein n is an integer of about 2≦n≦10, and wherein m is an integer of about 0≦m≦8; an extreme pressure additive consisting of a combination of (a) at least one of an alkyl phosphate and an aryl phosphate, and (b) a phenol compound, wherein the alkyl or aryl phosphite is represented by the formula:

wherein R⁶, R⁷, R⁸, R⁹, R¹⁰, and R¹¹ are each independently a C_(j)H_(2j+1) alkyl group exhibiting tertiary structures, where j is an integer of about 1≦j≦20, wherein the phenol compound is represented by the formula:

wherein R¹², R^(12′), R^(12″), and R^(12′″) are each independently a C_(p)H_(2p+1) alkyl group, and p is an integer of about 1≦p≦12; wherein R¹³, R^(13′), R^(13″), and R^(13′″) are each independently a phenol group represented by the formula:

wherein R¹⁴, R¹⁵, and R¹⁶ are each independently a C_(o)H_(2o+1) alkyl group and o is an integer of about 1≦o≦20, wherein R¹⁵ and R¹⁶ are tertiary structures; a surface fatigue life modifier comprising an alkyl thiocarbamoyl group represented by the formula:

wherein R¹⁷, R¹⁸, R¹⁹, and R²⁰ are each independently a C_(k)H_(2k+1) alkyl group and k is an integer of about 1≦k≦30, wherein R¹⁷, R¹⁸, R¹⁹, and R²⁰ optionally form a ring structure as combined together with the nitrogen atom to which they are bonded, where (A) is a chain of sulfur atoms, S_(n), or represented by the formula: S—(CH₂)_(m)—S and wherein n and m are integers of about 1≦n≦10 and about 1≦m≦6.
 26. The composition according to claim 25, wherein the antiwear additive, extreme pressure additive, friction modifier, and surface life fatigue modifier are present in an amount from about 10% or less by mole based on the total amount of lubricant, wherein the ratio of the friction modifier:antiwear additive:extreme pressure additive:surface fatigue life modifier is about 2:1:1:0.5. 